1. Field of the Invention
This invention relates to a structure of an X-ray mirror to be used for X-ray telescopes, X-ray microscopes, X-ray machining devices, and so on, and also it is concerned with a method for producing such X-ray mirror.
2. Discussion of Background
Conventionally, X-ray mirrors have been manufactured by the direct a vapor-deposition of a surface-smoothing thin film onto a substrate obtained from a material such as float glass, silicon wafer, polished glass, and so forth which can be machined to have very high surface smoothness (e.g., surface roughness [R.sub.max ] of 10 .ANG.) by the method of ion-beam sputtering, electronbeam deposition, laser-beam deposition, and so on. In the following, explanations will be given as to production of the X-ray mirror by the electron beam deposition method, in reference to "0 plus E", No. 88 (March 1987), pp. 67-73, by Yamashita as well as FIG. 5 of the accompanying drawing to the present application.
In the drawing, a reference numeral 1 designates a substrate, a numeral 4 refers to a crucible, a reference numeral 5 denotes electron beam for heating, a reference numeral 6 represents a shutter, a reference numeral 7 designates a thermo-couple, a numeral 8 refers to a film gauge, and a reference numeral 9 designates a vacuum container. Arrow marks indicate exit directions of exhaust gas. In the manufacture of the X-ray mirror by means of a device having such construction as mentioned above, the substrate to be used is chosen from float glass, silicon wafer, and so on, which can be rendered to have extremely smooth surface by the high precision machining such as float-polishing, etc. The material chosen as the substrate 1 is placed in the vacuum container 9, followed by evacuation of its interior. Thereafter, a deposition material such as, for example, Ni, Mo, Si, C, etc., which has been placed in the crucible 4, is heated by the heating electron beam 5 to a temperature, at which it attains a vapor pressure for the effective vapor-deposition. It is also possible that, by association of the shutter 6 with this heating electron beam source 5, the deposited film in a single or multi-layered structure may be distinctly formed. The temperature of the substrate can be monitored by the thermo-couple 7, and the film thickness can be checked by the film gauge 8.
Since the conventional X-ray mirror has been manufactured as mentioned above, and since the wavelength, with which the mirror is used, is within the X-ray range of several hundreds angstroms or shorter, it becomes essentially required that the film surface on the mirror should possess high smoothness (e.g., several tens of angstroms or below in terms of its surface roughness). On account of this, it was necessary to finish the surface of the coated film on the mirror to have high smoothness by means of a special machining method such as the float-polishing, elastic emission machining (EEM), and so on, the finishing methods of which were not so common. There was a further problem such that, while these machining methods were effective on those limited kinds of materials such as glass, silicon wafer, molybdenum, etc., they were not so effective on those fragile materials such as ceramics, etc., porous materials such as sintered bodies, etc., tough materials such as Fe, Al, Cu, etc., and other materials, with the result that arbitrariness in the selection of the material was extremely limited.
The nature of the problem inherent in the conventional methods can be said to have resided in the structure of the mirror per se, wherein the coating film is directly formed on the substrate.